This invention relates to a novel calixarene bisphosphite composition and its use in transition metal complex-catalyzed hydroformylation processes. As used herein, the term “hydroformylation” refers to a process of reacting one or more olefins with carbon monoxide and hydrogen in the presence of a hydroformylation catalyst to prepare one or more aldehyde products.
One important class of hydroformylation processes involves using a C4 butene stream as a raw material for hydroformylation to obtain C5 aldehydes, preferably, n-valeraldehyde. In some commercial operations, valeraldehyde is dimerized, and the dimerization product is hydrogenated to produce 2-propylheptanol or a mixture thereof with other alcohols, which find utility in the production of plasticizers. Alternatively, valeraldehyde may be hydrogenated to produce pentanol or amyl alcohol or mixtures of different C5 alcohol isomers thereof, any of which alcohols or alcohol mixtures may be used as a solvent. Valeraldehyde may also be oxidized to produce valeric acid or isomeric mixtures thereof, which may be used in synthetic ester lubricant products.
In the chemical art, the term “butene” or “butylene” generically refers to all hydrocarbon compounds having four carbon atoms and one carbon-carbon unsaturated double bond. Examples of specific butenes include butene-1, butene-2 (which includes cis and trans isomers), and isobutene (or isobutylene).
C5 aldehydes, such as valeraldehyde, are typically prepared by the hydroformylation of polymer grade butene-1, which is obtained through cracking petroleum and extensive purification procedures. In contrast, C4 raffinate feedstocks are a plentiful, less expensive source of C4 olefins as compared with polymer grade butene-1. As used herein, the term “C4 raffinate” or “C4 raffinate feedstock” refers to a C4 feedstream comprising a mixture of butene-1, butene-2 (cis and trans isomers), and isobutene. C4 raffinate feedstocks are obtained by thermal or catalytic cracking of hydrocarbon oils with subsequent treatment to remove butadiene, but otherwise with far less purification as is needed for polymer grade butene-1. Consequently, it would be advantageous to employ a C4 raffinate feedstock rather than polymer grade butene-1 in hydroformylation processes.
n-Valeraldehyde, which is a normal or linear product derived from butene-1, is preferred for many downstream end-uses. In contrast, due to branching, 3-methylbutyraldehyde, derived from isobutene, is an undesirable product, because it imparts inferior qualities to downstream products, particularly plasticizers. 2-Methylbutyraldehyde derived from butene-2 is an acceptable product. Moreover, at least a portion of butene-2 can be isomerized under hydroformylation reaction conditions to butene-1, which yields more of the normal or linear isomeric product. Given the effects on downstream products, it is advantageous to maximize the isomer ratio of normal to branched aldehydes (normal/branched or N:I isomer ratio) in the hydroformylation product stream.
The art, for example, WO-A1-2005/028407, discloses a hydroformylation of C4 raffinate feedstocks in the presence of a transition metal-organophosphorus ligand complex catalyst, wherein the ligand consists of an organophosphine or an organobisphosphite compound, to produce a product mixture comprising n-valeraldehyde, 2-methyl-butyraldehyde, and 3-methylbutyraldehyde. When isobutene is a significant component of the C4 raffinate feedstream (e.g., greater than 1 volume percent), typically, the N:I isomer ratio achieved is unacceptably low (<3/1). Moreover, insofar as is taught in WO 2005/028407, the rate of conversion of butene-2 is essentially identical to the rate of conversion of isobutene, which limits the extent to which the N:I isomer ratio can be improved.
One method of maximizing the N:I isomer ratio in the hydroformylation product involves removing undesirable 3-methylbutyraldehyde from the hydroformylation product stream; however, selective removal of one isomer from an isomeric mixture comprising valeraldehyde, 2-methylbutyraldehyde, and 3-methylbutyraldehyde involves difficult and expensive procedures.
Another method of maximizing the N:I product isomer ratio involves removing from the C4 raffinate feedstock the isobutene reactant from which the problematical 3-methyl-butyraldehyde is derived. U.S. Pat. No. 4,969,953 discloses the hydroformylation of raffinate I streams pretreated to remove butadiene as well as raffinate II streams pretreated to remove butadiene and isobutene. As the concentration of isobutene in the feedstream is lowered, the aldehyde product N:I isomer ratio is shown to increase. The skilled person generally recognizes that removing isobutene from a C4 raffinate is also a difficult and expensive procedure and, thus, also impractical.
In contrast to the above, separation of unconverted isobutene from a hydroformylation product mixture comprising C5 product aldehydes could be more readily achieved. Consequently, a need exists in the art for a catalyst that is capable of hydroformylating a C4 raffinate feedstock with increased conversion of butene-1 and butene-2 as compared with isobutene. Such a process would increase the N:I product isomer ratio while providing for reduced conversion of isobutene. The resulting hydroformylation product would comprise valeraldehyde, 2-methyl-butyraldehyde, unconverted olefins, primarily isobutene, and a reduced quantity of 3-methylbutryaldehyde. The separation of unconverted isobutene from the aforementioned hydroformylation product would be simple and cost effective.
The prior art discloses phosphorus-containing calixarenes and their use in hydroformylating a single olefin isomer, such as 1-octene, to the corresponding aldehyde, such as n-nonanal. Such art includes U.S. Pat. No. 5,717,126, as well as S. Steyer, et al., Dalton Transactions, 2005, 1301-1309; and C. Kunze, et al., Z. Anorg. Allg. Chem., 2002, 628, 779-787.